The invention relates to a method of manufacturing a colour television display tube having an apertured colour selection elctrode positioned a short distance in front of the display screen. The invention also relates to a colour television display tube manufactured according to such a method.
Such a method is disclosed in U.S. Pat. No. 3,475,169. In this method, first a conductive layer and then a photoconductive layer is provided on a window portion of the tube. The photoconductive layer is then uniformly electrically charged and subsequently exposed through the apertured colour selection electrode. In the exposed portions of the photoconductive layer the charge leaks away as a result of photoconductivity, whereas the charge is maintained in the unexposed portions. The electrostatic potential image obtained in this manner is developed by means of a suspension of phosphor particles or particles of a light-absorbing pigment in a nonpolar liquid. The particles in the suspension obtain a positive or negative charge by the addition of a surface-active stabilizer. The great advantage of this method is that both a positive and a negative reproduction of the potential image and hence of the pattern of apertures in the colour selection electrode can be obtained. The charged particles in the suspension used in the development of the latent image actually adhere on the regions whereafter the exposure charge remains if their charge is opposite to the charge of the photoconductive layer. If their charge is the same as the charge of the photoconductive layer, they just adhere between the charged regions of the potential image.
U.S. Pat. No. 2,848,295 discloses another method. In this method a photoconductive layer containing phosphor particles is provided on the window portion of the tube. In the unexposed state the layer is water-soluble and it becomes insoluble when exposed through the apertured colour selection electrode. The exposed portions of the light-sensitive layer become hardened and insoluble, whereas the unexposed portions remain soluble. The layer is then developed by rinsing with water as a result of which a phosphor pattern is obtained in the exposed portions of the photosensitive layer. According to U.S. Pat. No. 2,848,295, the exposure is not performed with light but with an electron PG,5 beam which is scanned across the colour television electrode and the window portion of the tube. The great advantage that this method has over the light exposure methods is that it obviates the need for correction lenses required in the latter to bring the virtual position of the light source in agreement with the position of the deflection point of the electron beams in the operating tube. Although the light exposure method has up to now been very common, it does not duplicate the paths of the electron beams in the final tube with sufficient accuracy. The path of the electron beam in an electron beam exposure method on the other hand, can in theory be identical and in practice substantially identical, to the path of the electron beams in the operating tube.